Calculating Kinetic Energy of a Running Cheetah

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Homework Help Overview

The discussion revolves around calculating the kinetic energy of a cheetah given its weight and speed. The original poster presents a problem involving the cheetah's weight of 419 N and speed of 112 km/h, questioning the correctness of their kinetic energy calculation.

Discussion Character

  • Exploratory, Mathematical reasoning, Assumption checking

Approaches and Questions Raised

  • Participants inquire about the units used in the calculations and the methods employed to derive the kinetic energy. There are discussions about converting speed from km/h to m/s and determining the mass from weight using the formula F=ma.

Discussion Status

Some participants have provided guidance on unit conversions and the relationship between weight and mass. There is an ongoing exploration of the calculations, with multiple interpretations of the problem being discussed. The original poster has indicated a resolution to their confusion regarding speed conversion.

Contextual Notes

There is a noted discrepancy regarding the units of the answers, with some participants questioning whether the options were in joules rather than km/h, which is typically a unit of speed rather than energy.

kajasu88
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Homework Statement


A cheetah whose weight is 419 N runs North at a speed of 112 km/h. What is the cheetah's kineticenergy? Is there a direction? Why or why not?

I got 2.68 x (10^5)
Is this wrong?
 
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What units are you using? How did you calculate it? Show what you did.
 
kajasu88 said:

Homework Statement


A cheetah whose weight is 419 N runs North at a speed of 112 km/h. What is the cheetah's kineticenergy? Is there a direction? Why or why not?

I got 2.68 x (10^5)
Is this wrong?

That does not see correct. If it weighs 419N, what is its mass? Convert 112km/h into m/s
 
i got the mass by dividing (419N)/(9.8m/s^2) because F=ma
then i plugged it into KE=(1/2)m(v^2)
V=112km/h (i left it in km/h b/c all the multiple choice answers were in km/h)
 
31.1m/s ??
 
kajasu88 said:
V=112km/h (i left it in km/h b/c all the multiple choice answers were in km/h)

The answers were in km/h? But that's a unit of speed, not energy. Are you sure they weren't in joules (symbol J)?
 
i figured it out!
so yes, 31.1 m/s
so KE=(1/2)m(v^2) ... (1/2)(419N / 9.8m/s^2)(31.1 m/s)^2
20,700 kg m^2/s^2

and i got the same answer as two other people
 

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